Continuous ceramic conveyor belts for use in processing items which need to be subjected to extremely high temperatures are known in the art. The ceramic belts convey the articles through a high temperature environment, or through other environments which would prove chemically destructive to metal or fabric belts. Prior ceramic belts have been made either entirely of ceramic material, or only partially of ceramic material. Belts made partially of ceramic material have a limited temperature range within which they can operate, while the configuration of belts made entirely of ceramic material have been limited by manufacturing difficulties.
U.S. Pat. No. 2,986,387 to Illing discloses a ceramic belt for use in carrying tile or other types of ceramic ware through a tunnel kiln which is fired at a high temperature. The ceramic belt is formed partially of ceramic material and includes individual ceramic links interconnected by refractory metal cross rods. The ceramic links are elongated and have rounded ends with apertures extending transversely through the links at opposite rounded ends. The links are disposed in cross rows in a staggered relationship such that the forward end of one link is disposed between the adjacent the rearward ends of two links disposed in the preceding row. Similarly, the rearward end of the first link is disposed between adjacent the forward ends of two other links disposed in the proceeding row. The apertures of the links are aligned to create a plurality of parallel cross-passages extending through the belt. Thus, the ceramic belt includes a plurality of columns or strips, each strip including a plurality of spaced links.
The refractory metal cross rods are disposed through the crosspassages, and have ends extending beyond the sides of the outermost links of the belt. A bore extends transversely through the rods at the extending ends. End caps are disposed on the extending ends of the rods, and include openings which are aligned with the corresponding bores in the rod. A refractory metal retaining pin is inserted in the opening and extends through the bore. An air-setting refractory cement is plugged into the opening over the end of the pin to prevent the pin from escaping from the bore after the cement matures. Insertion of the pins thereby holds the cap on the extending end to hold the ceramic belt together.
However, since the belt of Illing is made only partially of ceramic material, the temperature range in which the belt can be used is limited by the usable temperature range of the non-ceramic, refractory metal. For example, the operative temperature range of the refractory metal is disclosed in the Illing patent as 1600.degree.-2400.degree. F. However, current high temperature processing can occur up to 4000.degree. F. Thus, in the disclosed structure of Illing the metal pin would be likely to melt at the desired extreme temperatures. Furthermore, in order for the refractory cement to perform the function of preventing escape of the pin, it would have to be bonded in the hole or else the cement plug would simply fall out. In practice, it is difficult to bond cement material to ceramic material and operate at the temperature range of 4000.degree. F.
Belts made totally of ceramic material overcome the temperature limitations of partial ceramic belts. However, ceramic materials which are suitable for use at these elevated temperatures are extremely hard in the fired or usable state. Machining the components after firing to provide a conventional means of holding the belt assembly together is either impossible, or at best, extremely difficult and economically unfeasible. For example, due to the small size of the cross rods and their circular cross sections, it is extremely difficult to drill holes in the cross rods if a cotter pin mechanism is to be used.
Due to the difficulty of machining fired ceramic components, previous attempts to make ceramic conveyor belts have involved either machining an edge fixation into the components in their "green" or unfired state when the components are extremely fragile, or making a belt without a mechanism of holding the edges of the belt together. The width of a ceramic belt with components machined in the "green" state has been limited by the fragility of the "green" components which had to be of a relatively small size in order to be handled and machined without excessive breakage. Using "green" components has also resulted in large numbers of scrap pieces and has prevented the stocking of belt components or repair parts until after an order had been placed identifying the specific size of belt required. A drawback of running a belt with unconnected components is that the components may spread apart causing operational problems.
In addition to the above problems in forming end fixations on ceramic belts, reliability problems have occurred in prior ceramic belt end fixation techniques. For example, when a conventional mechanical interlock such as cotter pins or threaded nuts has been used, the pins and nuts frequently became loose after the belt was operated for a period of time. When glued or bonded components have been used, the reliability of the bond has been very limited in the high temperature range within which ceramic conveyor belts operate.